1. Field of the Invention
The present invention relates to a planar light-emitting device used to illuminate liquid crystal display panels as backlights and so on.
2. Description of the Related Art
Liquid crystal display devices to display images are widely used for displays of notebook personal computers, car navigation devices, mobile-type personal computers, mobile phones, personal digital assistances, automated teller machines and so on. A backlight unit is used for the liquid crystal display device and configured to irradiate light to a liquid crystal panel of the liquid crystal display device from a back side of the liquid crystal panel to enhance brightness of the liquid crystal panel.
There is known a backlight of a type using a light-guiding plate that guides light emitted from a light source having a fluorescent tube or light-emitting diode elements (hereinafter referred to as LED elements) and emits the light toward a liquid crystal display panel. Otherwise, there also is proposed a hollow-type illumination device configured to emit, reflect and diffuse light in a space between a light-reflecting member and a light-emitting member, without using the light-guiding plate.
For example, as disclosed in JP 2008-60061A and JP 2008-300194A there is proposed a hollow-type illumination device in which a light-reflecting member is disposed on a bottom surface of a hollow unit case, a light-emitting member is disposed on a surface of the unit case facing the light-reflecting member, a hollow light-guiding area is formed by a space defined between the light-reflecting member and the light-emitting member, and a light source comprises a plurality of LED elements arranged on a printed circuit board is disposed adjacent to the hollow light-guiding area to emit light emitted from the light source to the hollow light-guiding area. In the hollow-type illumination device, an LED collimator to collimate light emitted from the light source is disposed in a light-emitting part of the light source.
However, in the hollow-type illumination device as disclosed in JP 2008-60061A and JP 2008-300194A, although the light emitted from the light source by use of the collimator lens is collimated and emitted toward the hollow light-guiding area, light which cannot be focused by the collimator lens is emitted toward an upper portion and a downward portion, there is a problem that use efficiency of the light is reduced. Therefore, in the hollow-type illumination device as disclosed in the documents mentioned above, in order to focus as much as light, the collimator lens has a complicate special shape. Consequently, there is a problem that part cost is increased. Even in the special collimator lens, there is a limitation to focus light and the light that cannot be focused is emitted upward and downward.